Capacitance sensing systems can sense electrical signals generated on electrodes that reflect changes in capacitance. Such changes in capacitance can indicate a touch event (i.e., the proximity of an object to particular electrodes). Capacitive sense elements may be used to replace mechanical buttons, knobs, and other similar mechanical user interface controls. The use of a capacitive sense element allows for the elimination of complicated mechanical switches and buttons, providing reliable operation under harsh conditions. In addition, capacitive sense elements are widely used in modern customer applications, providing user interface options in existing products. Capacitive sense elements can range from a single button to a large number arranged in the form of a capacitive sense array for a touch-sensing surface.
Capacitive sense arrays and touch buttons are ubiquitous in today's industrial and consumer markets. They can be found on cellular phones, GPS devices, set-top boxes, cameras, computer screens, MP3 players, digital tablets, and the like. The capacitive sense arrays work by measuring the capacitance of a capacitive sense element and evaluating for a delta in capacitance indicating a touch or presence of a conductive object. When a conductive object (e.g., a finger, hand, or other object) comes into contact or close proximity with a capacitive sense element, the capacitance changes and the conductive object is detected. The capacitance changes can be measured by an electrical circuit. The electrical circuit converts the signals corresponding to measured capacitances of the capacitive sense elements into digital values. The measured capacitances are generally received as currents or voltages that are integrated and converted to the digital values.
There are two typical types of capacitance: 1) mutual capacitance where the capacitance-sensing circuit measures a capacitance formed between two electrodes coupled to the capacitance-sensing circuit; 2) self-capacitance where the capacitance-sensing circuit measure a capacitance of one electrode. A touch panel has a distributed load of capacitance of both types (1) and (2) and some touch solutions sense both capacitances either uniquely or in hybrid form with its various sense modes.